Electron memory tube



` m dr rr E WF T QN .eww E Dec. 2, 1958 Filed April 24. 195s INVENTOR MARCEL BARBIER BY ffl. 7

ATTO R N EY Dec., 2, 1958 M. BARBIER 2,863,089

ELECTRON MEMORY TUBE Filed April 24. 1953 5 Sheets-Sheet 2 INVENTOR MARCEL BARBIER ATTORNEY 5 sheets-sheet s INVENTOR M. BARBIER ELECTRON MEMORY TUBE MARCEL. BARBIER ATTO R N EY nrncraoN MnMoaY TUBE Marcel Barbier, Paris, France, assignor to Compagnie Generale de Telegraphie Sans Fil, Paris, France Application April 24, 1953, Serial No. 350,869

Claims priortiy, application France May 10, 1952 9 Claims. (Cl. 315-12) The present invention relates to image signal conversion or transformer tubes, known as electron memory tubes, for use in radar and television apparatus.

It is known from co-pending United States patent application Serial No. 347,019, filed April 6, 1953, for Electron Signal Storage Tubes to construct an electron optical system enclosed within a vacuum tight envelope comprising the following elements:

(1) A plane parallel dielectric plate in juxtaposition with a plane conducting or metallic plate, the dielectric material used for this purpose having a high resistivity.

(2) An electron gun inclined relatively to the axis of the plate and adapted to scan the plate by deflection of the beam emitted thereby.

(3) A plane grid parallel to the plate and having a strongly positive potential relatively to the potential of the plate and to that of the emissive cathode of the gun, thereby to accelerate the secondary electrons emitted by the plate under the impact of the electrons of the beam.

(4) An electron lens having its optical axis coinciding with the axis of the plate and the focal plane of which passes through the center of deflection of the gun, the potential of the lens being lower than that of the grid.

A system of this nature has for its purpose firstly to concentrate onto a collecting electrode raised to a suitable potential all the primary electrons which would normally be reflected by the plate as a consequence of the potential thereof. This collecting electrode is positioned in the focal plane of the lens but spaced from the axis thereof.

A further purpose of this system is to concentrate upon a collector which is co-axial with the tube and positioned at the focus of the lens the electrons produced by secondary emission on the plate surface by reason of the impact thereupon of the electron beam emitted by the cathode.

When this system is associated with suitable circuits it is possible by applying voltages of suitable values to the metallic plate to record at one and the same time on the surface of the plate an image comprising two colors in the form of electronic charges having positive or zero values and to repeat this image cyclicly for an indefinite time.

The image is inscribed by means of high speed electrons by raising the potential of the plate to a value where the rate of secondary emission thereof is greater than unity regardless of whether the beam is modulated. The image is read by slow electrons, the plate being brought to zero potential.

It should be appreciated that there are two possibilities in regard to the electrons reliected by the plate.

In the rst case, the electrons impinge upon a point of the surface having no charge and they are reected by mirror effect and focused by the lens onto the primary reflected electron collector. The initial velocity of these electrons being very high due to the high voltage applied to the grid, they are capable of passing through the voltage barrier established by the lens at the exit from the grid.

2,863,089 Patented Dec. 2, 1958 In the second case, the electrons impinge upon a positively charged point of the surface, which occurs when the bombardment is so adjusted that even when the plate voltage is reduced to zero the secondary emission is always greater than unity .at the points having a charge. The surface is, therefore, charged at the grid voltage and the reflected electrons reach the grid at low velocity and are stopped by the lens.

A system of this nature has the disadvantage that it cannot provide for simultaneous inscription and reading of the image which may be of interest in certain cases.

The present invention provides an electron memory tube which is free of this disadvantage.V

According to the invention, the electron optical system comprises, within a vacuum-tight envelope, the following elements, either alone or in combination:

(l) A plane parallel dielectric plate having one fac in contact with a plane metallic plate.

(2) A first electron optical system comprising an emissive cathode, a control grid and a gun having its axis inclined relatively to the axis of the plate, this system being positioned inside the envelope on the same side as the free face of the dielectric plate. The cathode of this system is raised to a fixed potential equal to that of the plate.

(3) A second electron optical lsystem comprising similar elements to those of the first system but having its gun aligned with the axis of the plate, this system being also positioned within the envelope on the same side of the free face of the plate. The cathode of this second systern is raised to a lower potential than the plate and the value thereof is such that bombardment of the plate by the electrons emitted by the second system gives rise to a secondary emission having a value greater than unity. Both electron optical systems comprise means for deecting the beams emitted thereby in order to scan the plate.

(4) A plane metal grid parallel to the plate and positioned between the plate and the two electron optical systems, the potential of the grid being high relatively to that of the plate, and the grid being in the close vicinity of the plate.

(5) An electron lens positioned between the grid and the electron optical systems having its focal plane passing through the deflection centers of both electron beams, the electron lens having for its purpose to enable the primary electrons emitted by the rst electron optical system inclined to the axis of the plate and reflected by the metallic plate to be collected by a collecting electrode spaced from the axis of the lens and positioned in the focal plane thereof.

According to the invention it is possible, with a mechanism similar to that described in the aforementioned copending application, to inscribe on the surface of the plate a series of signals in the form of positive electrical charges, the plate being bombarded, for this purpose, by electrons the velocity of which is such that the rate of secondary emission is greater than l, these electrons being emitted by the optical system positioned on the axis of the plate. These signals are then restored by bombardment with electrons having an impact Velocity such that the rate of secondary emission is less than l, these electrons being emitted by the optical system of which the gun is inclined to the axis of the plate. The respective voltages applied to the two cathodes must, of course, be suitably selected.

According to one embodiment of the invention, the vacuum-tight envelope comprises a glass envelope upon the internal surface of which is deposited a metallic coating. This envelope is raised to the same potential as ground.

The metal grid is at the potential of the envelope and :assenso The `electron lens comprises a metallic annulusr coaxialV with the platewhich in this embodiment is of disc shape, the dielectric plate in Contact therewith Ybeing of cylin drical shape and co-axial with the disc. The annulus is raised toa lowerpotentialthan the envelope and the collector is raised to a higher potential thanl the envelope.

'In another embodiment according to the invention, the electron lens is integral with the envelope, the grid being raised to a higherpotential than the envelope.

, Also in. accordance with the present inventio-n, the electron memory tube is associated with known circuits where.- by it is, possible to carry out the following preferred functions:

-(1) Inscribing on the surface of the dielectric plate aV beam at the same rhythmv as electrical signals of suitable shape, for example pulse signals.

Means known per se are provided for detlecting the beam thereby to scan all or part of the plate according to a desired scanningY standard having a predetermined lawy of space relationship and a predetermined time table. Such scanning may comprise sequential line scanning as in known television systems.

After scanning, the points Vof the'plate are divided into two classes smiliar to what is disclosed in the'aforementioned co-pending application in accordance with whether or not they have been subjected to the impact of electrons. The points which have not been subjected to Stich impact remain at the potential of the metallic plate. The other points, however, which have been subjected to the impact of electrons are raised to a fixed potential high enough relatively to the potential of the plate and close enough to the potential of the grid for the electrons emitted by the inclined electronoptical system to cause at these points a secondary emission at a rate greater than 1 as the result of a sufficient intensity of the inscribing beam.

The other electrical circuits, associated with the inclined electron optical system, comprise an output circuit associated with the collector of the tube, the purpose of this collector being to receive the primary electrons ref flected by those parts of the plate which are at the same potential as the cathode of the inclined optical system. There is also provided a detlecting device to enable scanningl of the plate by the beam emitted by the inclinedl optical 0r reading system in accordance with a given'space law and a predeter-minedgtime table. YThis deecting device is associated with meansfor reproducing this scanning either cyclicly or as desired.

,In the present application, the mechanisms for restoring readingV and inscribing the two color image are similar to those associated with the tube disclosed in the aforementioned co-p-ending application. The high velocity electrons are emitted bythe axial optical system and the slow electrons are emitted bythe inclined system, and

inscription and reading may be carried out simultaneously. This 1s becauseA the electrons issuing fromthe axial or inscribing gun give rise to secondary electrons which are accelerated by the grid' at the beginning of the inscrip-v tion and concentrated toward the center of deflection of the inscribing gun or which are stopped by the lens when the charged points have reachedv a potential suciently close to the potential of higher equilibrium.

(2) Inscribing the path of'movement of a moving tar get upon the plate; and preserving the record of its successive positions,such an operation being carrie-d out by means of the` same circuits as the preceding operation. The inscribed image can be, for example, the panoramic screen of a radar apparatus, the two colors being respectively the one produced by the echoes fro-m thereflecting targets and the other duer to the absence of such echoes. Means are provided for carrying out the cyclic restoration or restitution o-f such an image.

The echoes reflected from fixed objectives are superimposed upon each. other while-movingy targets leave on the plate a 'track representing their path or trajectory;`

be scanned in accordance with this rst standard. The

output of the `gun is then adjusted so that the positive chargesinscribedat a given point have for their consequence a sufficiently low potentialV for'. the electrons emitted. by. theV reading, gun to wipeV out the inscribed charges that are read.

The reading gun is associatedwithfmeans enablingthe,

beam to scan the plate in accordance with a second standard and the collector supplies ya known. videoV chain.`

Figure 1 is a diagrammatic illustration ofafirst em-l bodiment ofthe invention; y v

Figure 2 is a view similar to Figure 1 of a second embodiment of the invention; i

Figure 3.illustrates an example of a wiring diagram incorporating'a device accordingto4 the present inventionV for inscribing a two color image and for restoring or restituting it cyclicly, and

Figure 4 is a View similar to Figure 3 of a circuit for converting a television standard.

The laws of secondary emission are believed to be satisfactorily disclosed in the aforementioned co-pending application to which reference is made at this time in that respect in order toL avoidunnecessary repetition.

FigureV l is a longitudinal section through the planeof symmetry of a tube in accordance with a first embodiment of Vthe invention. In Figure 1, there' is shown a vacuum-tight envelope 1 having. an internal metal coating 6, and a laminar element or blade 2 of dielectric material, for example mica, juxtaposed to a metal plate 3 in relatively to that of the blade. ,I The distance between the plate Vand the grid is not of a critical naturebut for purposes of illustration it may be stated to tbe of the. order of one centimeter. The mesh of the grid defines areas which are less than the cross-section of the electron beams emitted within the tube. A first electron optical system I is positioned at the end of the envelope remote from the blade 2, the plate 3 and the grid 4, and it comprises electron emissive means including an accelerating anode or electron gun 7 positioned with its axis inclined relatively to the axis of the plate. The electron optical system I also comprises a cathode 5 having the same potential as the plate 3, a control grid 12 and a system of deflecting plates 8. The center of deile-ction of the electron beam emitted by the cathode 5 and the gun 7 is indicated at C1. An electron lens 9 comprising a metal annulus co-axial with the plate 3 occupies an intermediate position between the electron optical system I and the grid 4. This annulus is raised to a lower potential than the grid 4 but a higher 'potential'than the plate 3. The

structure of the electron lens is such as to provide a focal plane containing the point C1. The primary electrons emitted by the electron optical system I and reected by the blade 2 are concentrated upon an electrode 10 spaced fro-m the axis of the blade 2 and the plate 3 and positioned within the focal plane of the lens 9.

A second electron optical system II comprising similar elements to those of the rst electron optical system, namely a cathode 13, a control grid 14, an electron gun 15, and a system of deecting plates 16, is positioned co-axially with the plate 3. The cathode 13 of this second electron optical system is raised to a negative potential relatively to the plate 3 and this potential is so selected in absolute value as to be suicient fo-r the electrons emitted by the electron optical system II to reach the blade 2 at a velocity enabling a secondary emission rate having a value greater than 1. The center of delection C2 of the beam emitted by the electron optical system II is also positioned substantially within the focal plane of the lens 9.

Figure l also discloses a wiring diagram according l to which the envelope of the tube and the grid 4 are connected to ground. The lens 9 is raised to a lesser potential than ground, fo-r example of the order of 100 volts. The plate 3 and the cathode 5 are raised to a same negative potential of the order of 2,000 volts. The cathode 13 is raised to a potential corresponding to a secondary emission rate on the blade 2 having a value greater than 1, namely to a potential of the order of 2,100 volts relatively to ground.

The accelerating anodes 7 and 15 are raised, for example, to the same potential as the grid 4 or lens 9 and the control grids 12 and 14 are at a slightly lower potential than their respective cathodes.

The operation of a tube in accordance with Figure 1 closely resembles that of a tube in accordance with the aforementioned co-pending application.

The electron optical system II emits an inscribing beam. The difference of potential V1 between the cathode 13 and the plate 3 is greater than V1. If the potential of the cathode 13 is taken as the base reference for all voltages, then V1 is the plate voltage for which the electrons impinging upon the blade 2 give rise to secondary electrons by impact upon the blade 2 in a number equal to the incident or primary electrons. Stated another way, V1 is the voltage at which the rate of secondary emission is equal to l.

Positive charges will, therefore, appear on the blade 2 at the points of impact of the electrons emitted by the electron optical system II raising the potential of these points to a value V depending upon the number of electrons impinging upon each point.

The electron optical system I, on the contrary, has its cathode 5 at the same potential as the plate 3. Consequently the blade 2 acts as a mirror for the electrons emitted by the electron optical system I and striking upon those points of the blade the potential of which has not been raised by the electrons emitted from the electron Yso optical system II. Since the primary electrons from the electron optical system I all strike the blade 2 with a common incidence imparted thereto by the lens 9, they will be focused upon the electrode 10. The velocity of these electrons as they pass through the grid 4 which is proportional to Vg2 will be suicient for them to pass through the negative voltage barrier established by the lens 9 relatively to the grid 4.

At the points of the blade 2 which have been charged by the primary electrons of the electron optical system II, the blade 2 is at a potential V-v relatively to the cathode 5, v being the difference of potential between the two cathodes, the cathode 13 being at a negative potential relatively to the cathode 5. If V-v is greater than V1, the points charged by the electron optical system II will gain a positive charge and it is possible for them to reach the higher potential of equilibrium VE of Vthe blade 2, as has been more fully explained in connection with Figure l of the aforementioned co-pending application. If V-v is smaller than V1, the points which have been charged by the electron optical system II will lose their charge and will tend toward a potential which is the lower potential of equilibrium of the cathode S.

The Secondary electrons emitted from the blade 2 will have a path of movement substantially perpendicular to the plane of this blade.

Figure 2 illustrates a second embodiment of the invention wherein the electron lens 9 is incorporated in a wall of the envelope, namely in the internal metal coating thereof. In this embodiment, the grid 4 is at a higher potential than the envelope, the latter being grounded. The same reference numerals have been applied in this figure to similar parts already shown in Figure l.

Figure 3 illustrates diagramatically an apparatus including a tube according to the invention which enables a two color picture to be recorded in the form of positive electrical charges and which also enables this picture to be simultaneously restored or restituted. In this gure, there is shown diagrammatically a tube in accordance with Figure 1 and having the same reference numerals applied thereto. The control grid 14 of the electron optical system II is connected to a circuit 31 which is known per se and which supplies a constant positive voltage only under the influence, for example, of a device 32. In these circumstances, the electron optical system II is normally biased and will emit an electron beam only when a positive voltage is supplied to the electrode 14. The device 32 is connected, for example, to a known image analyser 33 which explores a two color picture 34, for example black and white, in accordance with a predetermined scanning cycle. This exploration is produced by means of a time reference device 35, for example a line sequential apparatus. Each white point of the image will produce an impulse upon the device 31 of xed shape and amplitude. The picture 34 being a two color picture in black and white excluding half tones, these impulses will unbias the electron optical system II, and since the device 35 is connected to the deflecting plates 16, the blade 2 will be scanned concurrently and simultaneously by the beam emitted by the electron optical system II.

There will appear on the blade Z a positive charge which will always have the same value each time the analyser encounters a white point and no charge will appear when it encounters a black point. It is, of course,

understood that the potential of the plate 3 relatively to the cathode 13 is suicient for the rate of secondary emission from the blade 2 resulting from the impact of electrons to be greater than 1.

If the output from the electron optical system II and the scanning frequency thereof are suitably adjusted, the charge caused by a white point will raise the potential of the corresponding point of the blade to a value U in the neighborhood of the scanning potential Vg. Thus there will be reproduced on the blade an image of positive electrical charges corresponding to the picture 34.

i The electron, optical' system I has its cathode 5 at the same;potentialv as the' plate 3, and since its control grid 1,2,- is at aglixed; potential this system will have a e011-, stant Output. rIfhedeecting plates 8; are connected to a known timereference device 36 determining the scanning frequency at which the blade 2 isV scanned by the beam emitted by the system I.

When the beam emitted by the system I; encounters. a point, having a charge U substantially equal to the charge V, the rate; of secondary emission resulting therefrom is greater thanfl, and the point will acquire an additional positive charge dU which will bring the potential of that point closek to the grid potential. The secondary electrons emitted during this operation will leave the blade 2 at; a low` initial velocity caused by the difference of potentialV Vgf-(U-l-dU). They will be stopped by the lens 9 which is at, a negative potential relatively to the potential Vg. lf the beam encounters a point which has n charge, there will be no secondary emission, this point being at the same potential as lthe cathode as is known from the aforementioned vco-p'ending application. The primary electrons will be reiiected by the blade bymirror elect and will be focused by the lens 9 on the collector 10 which is connected to a known receiving ldevice 37 the purpose of which is to reproduce the image.

The two .color picture 34 may be, for example, the image appearing on the4 panoramic screen of a radar apparatus,rthe white points or areas being those which represent targets or objects from whicha radar beam is reflected. `Generally speaking, these objects, are in motion, for example ships or aircraft, or stationary, for example coast lines, mountains, etc. The purpose of the device 33 is to perform cyclic scanning of the picture 34.

Between successive scannings, the objects in motion willhave changed position but the image thereof formed by the preceding scanning will have been retained on the blade and it is possible to record for an object in motion a succession of images representing the pathl of movement thereof. It will be appreciated that this characteristic property of the apparatus according to the invention may have a number of practical uses.

It should be noted that the reading beam may scan the blade at the same time as the inscribing beam which isV an improvement over the tube described in the aforementioned copending application. Furthermore,` the inscribing and reading beams do not have to scan the blade in synchronism.

Figure 4 illustrates how the characteristic properties of the, apparatus `according to the present invention may be put to use for solving a particular problem, Assuming that a certain television broadcast is based on a predetermined standard of a given number of lines per picture and a given number ofimages per second, it is, possible to receive this broadcast over a network of receivers operating according to a diterent standard. This problem would` be encountered if television programs were exchanged over the airways between diterent Vcountries having'adopted diterent standards. The tube according to the present invention offers a solution to this problem where the lines of the images are not interwoven orinterlaced but where the image frequency of the two standards is the same and the images are synchronized, and Figure 4 illustrates diagrammatically an example of a circuit for` carrying'out this form of the invention.

In Figure 4 there is shown a tube in accordance with Y FigureV l. The electron optical system II of this tube is shown with its control grid 14 connected to a video chain 41 receiving image signals in accordance with the first television standard S1. The density of the beam emitted by this system Il is modulated at the rhythm of the signals of S1. The deflecting plates 16 are connected to a time reference device s2 controlled by the chain i1 causing the beam to scan the blade 2 in accordance with the standard S1. Similarly to what has been stated in connection with Figure 3, the difference of potentiatbetween the plated; andthe cathode secondary emission of the blade 2 dueto the impact 'of' thev emitted electrons; t'o be Vgreater than 1. The outputf ofthe electronl optical system Il and` the; scanning; frequency, however, 'are so adjusted that the maximum charge deposited at a given point of the blade will raise the po-V tential 'ofy that point by anamount cV wherein dv is smaller than the potentialVl of the plate relatively to the Y voltage of the cathode '13 at which the rate of secondary emission is equal to l.

The electron optical system I scansl the plate in ac-` cordance with the standard S2. Asstatedy above the standard Sg'has the same image frequencyA as the standard S1 andthe scanning of the two systems is synchronized.

VScanning at the standard S2k is controlled by a knownv device acting upon the plates 8 of the electron optical system l. The reading beam emitted by the electron optical system I impinges upon points of the blade whichA have received a greater or lesser chargeV from the beam of the electron optical system II. This givesy rise to sec-,`

ondary electrons which are accelerated in a direction perpendicular to the grid 4 and concentrated by the lens 9 into the mouth ofthe electron system II so long as the point It is known that the restitution of an image by the absenceofcurrent in the reflected primary beam has sufficient tidelity for television purposes.l Thus, the collector l@ can -be used for supplying to a video chain 4 3 the necessary signal for retransmission.

What is claimed is:

1. Electron memory storage apparatus including aV memory tube having a vacuum tight enclosure and comprising, inside the enclosure: a plane laminar element of dielectric material having two parallel faces and an axis, a plane metallic plate in contact with one of said faces and the other face being free; a iirst electron optical system including an emissive cathode, afcontrol grid andan electron gun, the axis of said system being inclined to the axis'of said laminar element, and saidrsystern being directed toward said free face; means for maintaining at substantially the same xed'potential both the cathode of said system 'and saidgmetallic plate; ,al second electron optical system comprising electron emitting means including a cathode, having itsaxis coincident with the axis of said laminar element, said emittingmeans being directed toward said free face; means for maintaining the cathode of said emitting means at a `fixed potential below that of said plate, said last named means being so dimensioned that the bombardment of said laminar element by electrons emitted from said emitting means gives rise to a secondary emission rate having a value greater than unity; means for deiiecting the electron beam emitted from each said system and for defining a center of deflection for each said beam about which said beam scans said laminar element; a plane metal screen in close proximity to said free face'of said laminar element; means for raising the potential of said metal screen to a high positive value' relatively to the potential of said plate; an electro-n lens occupying an intermediate position between said metal screen and said electron optical systems, said lens being co-axial with said plate and deining a focal plane containing the respective centersof said systems; means for raising said lens to a potential slightly below that of said metal screen relatively to said plate; a collector electrode Y spaced from the axis of said lens and positioned in the focal plane thereof;v and l,means for applying to said coll'S. is 'sullcientfor-the. rate of-V lector electrode substantially the same potential as said metal screen.

2. An electric circuit apparatus according to claim 1, and further comprising in combination: means connected to the control grid of said second electron optical system, for controlling the intensity of the beam emitted thereby; means for causing the beam emitted by said second electron optical system to scan at least a part of said laminar element in accordance with a rst scanning standard; means for causing the beam emitted by said rst electron optical system to scan said part of said laminar element, in accordance with a second scanning standard; and an output circuit connected to said collector electrode.

3. Apparatus as claimed in claim l wherein said vacuum tight enclosure comprises an envelope of dielectric material having a thin metallic coating on the internal surface thereof.

4. Apparatus as yclaimed in claim l comprising a source of potential for applying ground potential to said envelope and to said metal grid, for applying a potential of the order of -100 volts to said lens, for applying a potential of -2000 Volts to said plate and to the cathode of said rst electron optical system, for applying to the cathode of said second electron optical system a potential of the order of 100 volts relatively to said plate and for applying a potential of the order of 100 volts to said collector electrode.

5. Apparatus as claimed in claim 1 wherein said electron lens comprises an annular metal ring co-axial with said plate, said plate being of disc shape and said laminar element being of cylindrical shape co-axial with said disc, means being provided for applying a potential of the order of 100 volts to said lens relatively to said screen.

6. Apparatus as claimed in claim 1 wherein said electron lens is integral with said metallic coating, said metallic coating being at ground potential and means being provided for applying a potential of an order of 100 volts to said metal screen.

7. Apparatus according to claim l for inscribing a two color image on the surface of said dielectric laminar element by depositing electrical charges of iixed value upon discreet points of said element and for cyclic restitution of said image comprising further, in combination: a tube, means connected to the control grid of said second electron optical system for interrupting the beam emitted thereby in synchronism with a train of electrical signals of selected form; means for causing the beam emitted by said second electron optical system to scan at least part of said laminar element in accordance with a first scanning standard; means for controlling the intensity of the beam emitted by said second electron optical system whereby the points of said laminar element scanned by said beam and subjected to the impact of the electrons thereof are raised to a potential causing the electrons emitted by said first electron optical system to produce at said points a secondary emission at a rate greater than unity; an output circuit connected to said collector electrode; and means connected to said rst electron optical system for causing the beam emitted thereby to scan at least part of said laminar element in accordance with a second scanning standard.

8. Apparatus as claimed in claim 7, including means for inscribing on said laminar element a track corresponding to 'the path of movement of an object in motion and for preserving the track inscribed in accordance with successive positions of said object.

9. Apparatus according to claim l for converting the standard of a televised image and further comprising, in combination: a tube; a video chain associated with the control grid of said second electron optical system for intensity modulating the beam emitted thereby in synchronism with signals received through said chain in accordance with a first standard; means for causing the beam emitted by said second electron optical system to scan said laminar element in accordance with said rst standard; means for controlling the intensity of said beam whereby the charges deposited at each point of said laminar element are at a potential causing the electrons emitted by said rst electron optical system to wipe out said charges for producing a secondary emission at a rate less than unity; means for deflectiug the beam emitted by said rst electron optical system in accordance with a second television standard; and a video transmitting chain connected to said collector electrode.

References Cited in the le of this patent UNITED STATES PATENTS 2,464,420 Snyder Mar. 15, 1949 2,563,500 Snyder Aug. 7, 1951 2,570,858 Rajchman Oct. 9, 1951 2,706,246 Klemperer Apr. 12, 1955 2,711,289 Zworykin June 21, 1955 2,728,020 Pensak Dec. 20, 1955 

